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How ideCAD defines accidental torsion according to ASCE 7-16?

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There are two different ways to determine the additional eccentricity effect.

1- Static procedure: For horizontal earthquake loading situations, the torsional moment (M_z) obtained by multiplying the story forces determined by response spectrum analysis by the rate of eccentricity is applied to the center of the diaphragm. Regardless of whether the diaphragm type is full or semi-rigid, Torsion Moment is applied to the center of the diaphragm in all floors containing diaphragms. As of V10.15, it It is applied if the static eccentricity and single loading state calculation method is selected in the analysis settings tab. Unless a different value is entered in the analysis settings tab, transactions are made according to the (+) and (-) 5% eccentricity ratio in both horizontal directions.

2- Dynamic procedure:  Determined directly for each mode by response spectrum analysis. It is included in the internal force and displacements of the horizontal earthquake loading conditions obtained by combining with the CQC  or  SRSS methods method. According to the method, at each node where the masses are distributed, the mass at the center of the diaphragm, for the semi-rigid diaphragm, or the mass at the center of the diaphragm, is calculated by shifting (+) and (-) 5%. Since it is obtained by shifting the mass matrix, 4 four different modal analyzes are required in the standard procedure.

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